1. Field of the Invention
The present invention relates to a compressor, and in particular to an apparatus and a method for controlling a compressor which are capable of making a compressor have an optimum efficiency even in a maximum load state.
2. Description of the Prior Art
Generally, because a linear compressor does not include a crankshaft converting a rotation motion into a linear motion, the linear compressor shows a less resistance loss than a resistance loss in a general compressor, accordingly the linear compressor is superior than the general compressor in a compressing efficiency aspect.
When the linear compressor is used for a refrigerator or an air conditioner, a freezing capacity of the refrigerator or the air conditioner can be controlled by varying a compressing ratio of the linear compressor by varying a voltage applied to the linear compressor. The above-mentioned linear compressor will be described with reference to the accompanying FIG. 1.
FIG. 1 is a block diagram illustrating a construction of an apparatus for controlling a linear compressor.
As depicted in FIG. 1, the apparatus for controlling the linear compressor includes a linear compressor 13 varying an internal stroke (not shown) by being inputted a voltage supplied to an internal motor according to a stroke reference value and adjusting a freezing capacity by moving an internal piston up and down, a voltage and current detecting unit 15 detecting a voltage and a current generated in the linear compressor 13 according to the variation of a stroke, a stroke calculating unit 14 calculating a stroke by using the detected voltage and current, a comparator 11 being inputted the calculated stroke and a stroke reference value, comparing the two strokes and outputting a comparison value, and a stroke controller 12 increasing or decreasing a voltage inputted to the motor according to the comparison value. The operation of the apparatus for controlling the linear compressor will be described in detail.
First, the linear compressor 13 is inputted a voltage supplied to the motor and varies a stroke according to the stroke reference value set by a user and adjusts a freezing capacity by moving the piston up and down according to the variation of the stroke. Herein, the stroke means a distance in which the piston of the compressor 13 moves while performing a reciprocating motion.
The voltage and current detecting unit 15 detects a voltage and a current generated in the linear compressor 13 according to increase of the stroke due to the voltage applied to the motor and outputs the detected voltage and current to the stroke calculating unit 14.
The stroke calculating unit 14 calculates an actual stroke by using the detected voltage and current. In more detail, the actual stroke and a velocity of the piston can be calculated with an inductance of the motor, a motor constant, the detected current and the voltage. It can be described as below equation 1.                               Velocity          =                                    V              m                        -                                          R                ac                            ⁢              I                        -                          L              ⁢                                                ⅆ                  i                                                  ⅆ                  t                                                                    ,                  xe2x80x83                ⁢                  Stroke          =                                    1              α                        ⁢                          ∫                                                (                  Velocity                  )                                ⁢                                  ⅆ                  t                                                                                        Equation        ⁢                  xe2x80x83                ⁢        1            
Herein, Vm is a voltage detected at both ends of the motor of the linear compressor, I is a current applied to the motor, L is an inductance of the motor, xcex1 is a motor constant. Herein, the motor constant is a constant value of the motor converting an electrical power into a mechanical power, and the constant value has been determined in designing of the motor.
After, the comparator 11 is inputted a stroke reference value and a stroke value calculated in the stroke calculating unit 14 and applies a comparison value to the stroke controller 12. Herein, the stroke controller 12 varies a voltage applied to the motor according to the comparison value and outputs the varied voltage to the linear compressor 13.
When the stroke calculated in the stroke calculating unit 14 is smaller than the stroke reference value, the stroke controller 12 increases the voltage inputted to the motor, when the stroke calculated in the stroke calculating unit 14 is greater than the stroke reference value, the stroke controller 12 decreases the voltage inputted to the motor.
In the meantime, in the operation of the linear compressor, a maximum load can occur in the linear compressor 13, the maximum load is generated when power is initially applied to the linear compressor 13. It will be described with reference to the accompanying FIG. 2.
FIG. 2 is a wave form diagram illustrating a load in an initial operation of a linear compressor according to the prior art.
As depicted in FIG. 2, a maximum load works on the linear compressor 13 of the refrigerator when 10 minutes is passed after a power switch of a refrigerator is on initially, later the load is gradually decreased.
Accordingly, because even one abnormal operation can damage the internal motor, the maximum load has to be regarded in designing of the internal motor (not shown) of the linear compressor 13.
However, by regarding the maximum load in designing of the motor, a cost in the motor design is increased and a size of the motor is increased.
On the contrary, the motor is designed without regardless of the maximum load, when the motor can not stand a load, a flux saturation phenomenon serially occurs, accordingly the linear compressor can be damaged.
As described above, in the linear compressor according to the prior art, when the motor is designed regardless of the maximum load, the motor does not stand the load, the flux saturation phenomenon serially occurs, accordingly the linear compressor can be damaged.
In addition, in the linear compressor according to the prior art, when the motor is designed by regarding the maximum load, a cost in the motor design is increased.
In addition, in the linear compressor according to the prior art, when the motor is designed by regarding the maximum load, a size of the motor is increased.
Accordingly, it is an object of the present invention to provide an apparatus and a method for controlling a compressor which are capable of making a linear compressor have an optimum efficiency even in a maximum load condition.
In order to achieve the above-mentioned object, in an apparatus controlling a motor by being inputted power, there is provided an apparatus for controlling a compressor in accordance with the present invention including a maximum stroke value determining unit varying and outputting a pre-stored stroke reference value by comparing a maximum stroke value with an actual stroke value and a linear reciprocating compressor controlling power applied to an internal motor according to the varied stroke reference value.
In order to achieve the above-mentioned object, in a method for controlling a motor by being inputted power, there is provided a method for controlling a compressor in accordance with the present invention including outputting a comparison value by comparing a maximum stroke value with an actual stroke value, varying a pre-stored stroke value according to the comparison value, and controlling a voltage inputted to the motor according to the varied stroke reference value.